1. Field of the Invention
The present invention relates to antennas and, in particular, to antennas formed of a plurality of planar antennas.
2. Description of Related Art
Antennas are used for wireless coupling of data transmission devices. Depending on the field of application, antennas having special characteristics are selected. Thus, compromises must be made, taking integrability, gain, noise or the bandwidth of an antenna into account. One of the decisive selection factors is the feed method of the antenna used. We differentiate between differential and single-ended feed.
When a differential signal routing is used in an antenna amplifier for a higher gain, lower noise or more simple design, a differentially fed antenna, such as, for example, a dipole antenna, should be selected ideally. Instead, a symmetry transformer, which is also called balun, transforming from a differential signal routing to a single-ended signal routing may be employed. In practice, the decision of the feed method determines the type of the antennas used or alternatively the usage of a symmetry transformer.
The dipole antenna or similar differentially fed antennas have the disadvantage that they must not have a ground area or metal area next to them and often are not integrable. The usage of a planar antenna, such as, for example, a patch antenna, allows improved integrability, but requires a symmetry transformer which may consume a considerable amount of space.